Characteristics and Applications of Check Valves

A check valve is a type of directional control valve in a hydraulic system. Its main function is to restrict the flow of hydraulic fluid to only one direction, preventing reverse flow. Check valves have a simple structure and working principle, yet they are one of the most widely used components in hydraulic systems. Correct selection and proper application of check valves not only meet the diverse functional requirements of hydraulic systems in different applications but also simplify hydraulic system design. This article introduces the typical applications and usage precautions of check valves in actual hydraulic systems.

1. Classification and Characteristics of Check Valves

Check valves are generally classified into two types according to their structural characteristics: ordinary check valves and pilot-operated check valves. The graphic symbol for an ordinary check valve is shown in Figure 1a; its function is to allow fluid flow in only one direction (from A to B) and not in the reverse direction (from B to A). The graphic symbol for a pilot-operated check valve is shown in Figure 1a below; its function is to allow fluid flow in one direction (from A to B), while reverse flow (from B to A) must be achieved through control oil (C).

The performance requirements for check valves mainly include: low resistance (i.e., low pressure loss) when hydraulic fluid flows through the check valve; good sealing and no leakage when hydraulic fluid flows in the reverse direction; and no vibration, impact, or noise during operation.

2. Applications of Check Valves

1) Protecting the Hydraulic Pump

As shown in Figure 1b, the check valve 3 is installed at the outlet of the hydraulic pump 1 to prevent a sudden increase in system pressure (such as pressure relief from the accumulator 4) from being transmitted back to the hydraulic pump, preventing pump reversal or damage, thus protecting the hydraulic pump.

2) Preventing Interference in Oil Circuits

As shown in the dual-pump oil supply system in Figure 1c, when the system pressure is low, the oil output from pumps 1 and 2 merges to supply the system, meeting the need for a large system flow rate. When the system pressure exceeds the set pressure of the unloading valve 5, the low-pressure pump 2 unloads, and only the high-pressure pump 1 supplies oil to the system. At this time, the check valve 4 separates the high-pressure oil circuit and the low-pressure oil circuit, preventing mutual interference.